When a print control apparatus executes composition processing, a display list is generated by sorting a plurality of pieces of vector information that describe contour data of graphics objects that form a page on the basis of vector start coordinates. Also, a display list is generated using fill information of graphics objects that form a page as multilevel data corresponding to the vector information. Furthermore, upon transforming the display list into raster data, raster data is generated in the order of sort directions on the basis of the sorted vector information in the display list. Furthermore, upon transforming the display list into raster data, when composition processing between graphics objects is included, it is executed using only fill information that influences final output pixels. In such a print control apparatus, the composition processing is always done using multilevel data. Moreover, color space conversion and halftoning processing are executed after composition. This is because the Raster Operation (to be abbreviated as ROP hereinafter) of Windows® is premised on composition processing for multilevel data.
Note that the ROP processing is logical operation processing to be executed when two or more objects (raster images) overlap each other. By executing the ROP processing, not only two or more objects are overwritten with depth ordering, but also effects of watermarking, inversion, and the like can be given. ROP2 of Windows® executes a logical operation of two objects, i.e., a source (a new image to be written) and destination (original image; an already written image). These instructions execute logical operation processing such as AND, OR, NOT, XOR, and the like for respective objects, and write the result in the destination. With the ROP2, 16 different types of logical operation processing are available depending on the combinations of the states of respective drawing objects and output results.
On the other hand, raster data is generated from a display list before the display list for one page is generated due to an insufficient memory used to store a display list, and a display list using the generated raster data as a background of a page is often generated.
In such a print apparatus, for example, when the fill information of the display list stored as the background is multilevel data, the display list size becomes large, and the problem of an insufficient memory cannot be sufficiently solved. If a sufficiently small data size is to be attained by multilevel data compression (e.g., JPEG or the like) so as to reduce the display list size, image quality deteriorates consequently, and the quality drop of a printed image becomes conspicuous.
When data undergoes halftoning processing to reduce the data size of the background, multilevel data and halftone data must be composited upon processing the ROP of Windows® as composition processing. Since the ROP of Windows® is premised on multilevel processing, troubles upon composition must be minimized.
It is, therefore, an object of the present invention to allow raster generation with a small memory size and high image quality and to minimize troubles upon composition even when a display list is generated as a background due to an insufficient memory used to store the display list.